Various types of detectors are known for detecting intrusion to protected regions. These include, among others, infra-red detectors, which detect infra-red emissions from persons or other objects; microwave detectors, which normally detect doppler signals produced by the motion of an object in an electromagnetic field containing microwave energy; and, ultrasonic detectors, which emit ultrasonic energy pulses intermittently to the protected region, form a reference pattern of reflections from the protected region, compare a current reflected pattern with the reference pattern, and activate an alarm when the two patterns are significantly different.
Typical examples of ultrasonic intrusion detectors which operate in the manner indicated above are U.S. Pat. No. 4,382,291, dated May 3, 1983, U.S. Pat. No. 4,499,564, dated Feb. 12, 1985 and U.S. Pat. No. 4,639,902, dated Jan. 27, 1987. Such ultrasonic intrusion detectors generally suffer from common disadvantages relating to the fact that they tend to generate false alarms due to spurious noises (e.g., ringing telephones, bells, buzzers and the like; noisy vehicles passing by near the protected region; moving air currents within the protected region; and, moving articles and personnel within the protected region).
It is, therefore a primary object of the present invention to provide an improved intrusion detection apparatus and method in which the number of false alarms generated by spurious noise and non-intruder-originated movements in the protected region is significantly reduced from the number of spurious false alarms generated by prior art ultrasonic intrusion detection apparatus and methods.
Another major object of the present invention is to provide an intrusion detection apparatus and method which employs real time integration in its control circuitry to increase the probability of and to improve the repeatability of detection signals generated therein.
A further object of the present invention is to provide an intrusion detection apparatus and method wherein the user may exclude from protection selected zones within the protected region.
An additional object of the present invention is to provide an intrusion detection apparatus and method having the capability to automatically compensate for and ignore ambient environmental changes.
Yet another object of the invention is to provide an intrusion detection apparatus and method that can detect, and provide signals to inform the user of, attempts to mask or block the operation of the apparatus.
Further objects and advantages of this invention will become apparent as the following description proceeds.